A comparative study of Vitamin E TPGS/HPMC supersaturated system and other solubilizer/polymer combinations to enhance the permeability of a poorly soluble drug through the skin

In transdermal drug delivery systems (TDDS), it is a challenge to achieve stable and prolonged high permeation rates across skin, because the concentration of the drug dissolved in the matrix has to be high in order to maintain zero order release kinetics of the drug. In case of poorly soluble drugs, due to thermodynamic challenges, there is a high tendency for the drug to nucleate immediately after formulating or even during storage. The present study focuses on the efficiency of vitamin E TPGS/HPMC supersaturated solution and other solubilizer/polymer systems to improve the solubility of the drug and inhibit crystal growth in the transdermal formulation. Effect of several solubilizers, for example, Pluronic F-127, vitamin E TPGS and co-solvent, for example, propylene glycol (PG) were studied on the supersaturated systems of ibuprofen as model drug. Various stabilizers such as hydroxylpropyl methylcellulose (HPMC 3 cps) and polyvinylpyrrolidone (PVP K-30) were examined to evaluate their crystal inhibitory effects. Different analytical tools were used in this study to detect the growth of crystals in the systems. Vitamin E TPGS and HPMC 3 cps formulation produced the highest permeation rate of the drug as compared to other systems. In addition, the onset of crystallization time was shown to be longer with this formulation as compared to other solubilizer/polymer combinations.     

Asymmetric ion track nanopores for sensor technology. Reconstruction of pore profile from conductometric measurements

We reconstruct the profile of asymmetric ion track nanopores from an algorithm developed for conductometric measurements of symmetric nanopores. The validity of the reconstruction is supported by FESEM observations. Our analysis reveals that asymmetric pores fabricated by one-sided etching are funnel-like and not conical. The analysis provides the constriction diameter and the pore profile as a function of etching time. The reconstruction of the pore profile defines the starting conditions of asymmetric nanopores at breakthrough. The deviation from the conical shape is most pronounced at the pore tip. This critical zone dominates transport properties relevant to ion conductance, selectivity, current rectification, resistive pulse sensing and biosensors. The classical cone approximation used until now underestimates the tip diameter by a factor of two. As transport processes in nanopores depend in a highly nonlinear way on the constriction diameter the presented reconstruction must be taken into account when studying ionic and molecular transport processes in asymmetric pores.     

Studies on the impact of glycation on the denaturation of whey proteins

It could be shown for technologically relevant whey protein powders that denaturation of β-lactoglobulin (β-Lg) is affected significantly by the extent of covalent modification of lysine residues by lactose. The amount of acid soluble β-Lg as measured via RP-HPLC with UV detection after heating for 10 min at 80 °C increased from 40% (4.6% lysine modification) to 82% (22.4% lysine modification). An increase in glycation leads to a slower denaturation-induced oligomerisation, as shown by SDS-PAGE. Concomitant with an increase in lysine modification, the denaturation temperature increased from 79.5 to 84 °C, as measured by differential scanning calorimetry (DSC). Covalent attachment of lactose to whey proteins during preparation or storage significantly improves the heat stability of whey proteins, which may be of particular importance for the technological use of whey proteins varying in the degree of lysine modification.     

An Automatic Hierarchical Delay Analysis Tool

The performance analysis of VLSI integrated circuits(ICs) with flat tools is slow and even sometimes impossible to complete.Some hierarchical tools have been developed to speed up the analysis of these large ICs.However,these hierarchical tools suffer from a poor interaction with the CAD database and poorly automatized operations.We introduce a general hierarchical framework for performance analysis to solve these problems.The circuit analysis is automatic under the proposed framework.Information that has been automatically abstracted in the hierarchy is kept in database properties along with the topological information.A limited software implementation of the framework,PREDICT,has also been developed to analyze the delay performance.Experimental results show that hierarchical analysis CPU time and memory requirements are low if heuristics are used during the abstraction process.     

A dynamic reconfiguration scheme for mega bit Static Random Access Memories

The objective of this paper is to present a novel dynamic reconfiguration scheme for mega bit Static Random Access Memories (SRAMs). Most of the conventional reconfiguration methods are implemented using two-way switching elements. The proposed scheme is based on on-chip word failure detection and reconfiguration to spare word cell using multi-valued logic elements. The physical concept of the dynamic reconfiguration scheme and implementation details are discussed. Based on the SRAM dynamic reconfiguration implementation a reliability model is develoed. Dyanamic reconfiguration scheme reliability comparisons with other existing methods are presented. The advantages of the proposed dyanamic reconfiguration scheme are highlighted.     

Effect of nanopore geometry on ion current rectification

We present the results of systematic studies of ion current rectification performed on artificial asymmetric nanopores with different geometries and dimensions. The nanopores are fabricated by the ion track etching method using surfactant-doped alkaline solutions. By varying the alkali concentration in the etchant and the etching time, control over the pore profile and dimensions is achieved. The pore geometry is characterized in detail using field-emission scanning electron microscopy. The dependence of the ion current rectification ratio on the pore length, tip diameter, and the degree of pore taper is analysed. The experimental data are compared to the calculations based on the Poisson-Nernst-Planck equations. A strong effect of the tip geometry on the diode-like behaviour is confirmed.     

A Unity Gain High Speed Buffer to Improve Signal Integrity in High Frequency Test Interface

The availability of faster electronic components allows the design of more effective and efficient test equipments. However in high-speed applications, the effect of interconnects between the tester and the device under test DUT introduces ringing, overshoot and timing delay problems. In this paper we present an output high speed buffer which helps to cancel the overshoot, undershoot, and ringing. The buffer which has a unity gain, presents a high output current and introduces small delay. It is able to drive the comparator of the tester through the transmission line with minimum distortion of the signal. Compared with other approaches, the use of this output buffer provides good improvement of the signal. This output buffer which is designed for the interface between tester and DUT can be considered for communication between high speed devices in printed circuits boards. The calibration procedure is explained in order to determine the delay introduced by the buffer and to measure low and high voltage levels of the digital output signal of the buffer.     

The amine modified acrylonitrile-divinylbenzene copolymers in the phase transfer catalysis

Summary Amine modified, macroporous acrylonitrile-divinylbenzene copolymers of various crosslinking degree were used as catalysts in the reaction of octylbromide with cyano anions.The dependence of their catalytic activity upon swelling and strongly basic amino groups content were discussed.The reaction rate constants were somewhat lower than those for the reactions catalysed by other polymers containing tributylammonium groups.lt was probably due to the presence of ordered regions in copolymers containing large amounts of acrylonitrile units.This work was presented in part at the 30th Microsymposium on Macromolecules, Prague, July 1987     

Dielectric and TSC study of semicompatible PVDF/PMMA blends

Summary Dielectric and TSC studies of charged (by stabilized electrical breakdown) and discharged PVDF/PMMA blends have been performed. The relative changes in are found to decrease with increasing PVDF content except for samples with 50 and 70 weight-% of PVDF. The temperature T_max of the TSC maximum is found to be shifted linearly towards lower temperatures with increasing PVDF content up to 30 weight-% of PVDF. For higher concentrations T_max is found to be independent on PVDF content except for samples of 70 weight-% of PVDF. These behaviours indicate that for PVDF concentrations higher than 30 weight-% the system starts to lose its compatibility.